Docker is an open source infrastructure management platform for running and deploying software. The Docker platform is constantly evolving so an exact definition is currently a moving target.
Docker can package up applications along with their necessary operating system dependencies for easier deployment across environments. In the long run it has the potential to be the abstraction layer that easily manages containers running on top of any type of server, regardless of whether that server is on Amazon Web Services, Google Compute Engine, Linode, Rackspace or elsewhere.
What is Docker and When to Use It clearly delineates what Docker is and what it isn't. This is a good article for when you're first wrapping your head around Docker conceptually.
Andrew Baker presented a fantastic tutorial at PyOhio on beginner and advanced Docker usage. Andrew also created O'Reilly Introduction to Docker video that's well worth buying.
Hosting Python WSGI applications using Docker shows how to use Docker in WSGI application deployments specifically using mod_wsgi.
How to Containerize Python Web Applications is an extensive tutorial that uses a Flask application and deploys it using a Docker container.
Deploying Django Applications in Docker explains some of the concepts behind using Docker for Python deployments and shows how to specifically use it for deploying Django.
A Docker primer – from zero to a running Django app provides specific commands and expected output for running Django apps with Docker and Vagrant.